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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

HARD  LEAD

249

95% alcohol until the reaction is neutral, and subsequently dried, heated in
an air-bath, cooled in a desiccator and weighed : PbS04 x 0-6831 = Pb.

2.  Determination of the Antimony.—The 50 c.c. of solution taken
is concentrated to 20-30 c.c., neutralised with 50% sodium hydroxide
solution, an excess of 3-4 c.c. of the latter and 30 c.c. of sodium sulphide
solution (D 1-225) added and the liquid heated and, after some tune, filtered
to remove the copper sulphide, etc., directly into a tared Classen capsule ;
the precipitate is washed with hot water in which a little sodium sulphide
is dissolved.    The nitrate is treated with 50 c.c. of sodium sulphide and
5-6 grams of pure potassium cyanide, mixed and electrolysed to determine
the antimony,   ND100 = o-i5-o-i8   amp., voltage = 1-1-2,   duration (o'l-
0-15 gram Sb) 15-18 hours.    When the deposition is complete, the capsule
is emptied, thoroughly washed with water, alcohol and ether, dried at 70°
and weighed.

3.  Determination of the Tin and Copper.—The 100 c.c. of solution
taken is rendered slightly alkaline with ammonia, treated with 5 grams
of oxalic acid, heated to obtain a clear solution, treated with 7 grams of
ammonium oxalate, and kept boiling for about an hour while a stream of
hydrogen sulphide is passed to precipitate the antimony and copper.   When
the liquid has cooled somewhat in the current of hydrogen sulphide, it is
filtered into a half-litre beaker, the filter being washed with a hot i% oxalic
acid solution saturated with hydrogen sulphide.

(a)  DETERMINATION OF THE TIN.   The filtrate is treated with 30 c.c.
of cone, hydrochloric acid and 20 grams of ammonium oxalate and boiled
for a short time to expel hydrogen sulphide.   After the liquid has cooled
somewhat, a few drops of 30% hydrogen peroxide are added and the solu-
tion heated for a little while, made up to 300 c.c., cooled to 40-45° and—
often turbid with sulphur—electrolysed to determine the tin :   coppered
Winkler cathode, spiral anode, ND100 = I amp., voltage = 3-4,  tempera-
ture = 40-50°,  duration  (o-i-0'3 gram Sn) = 4-5 hours  (see also Elec-
trolytic Determination of Tin in Ordinary Bronzes).

(b)  DETERMINATION  OF THE  COPPER.   The precipitated  copper and
antimony sulphides, which have been filtered off, are heated gently with
i% sodium hydroxide solution and filtered, the filter being thoroughly
washed with water faintly alkaline with sodium hydroxide ;   the copper
sulphide remains undissolved.    The filter-paper and precipitate are dried
in a small dish, the filter incinerated, the residue dissolved in nitric acid,
and the copper determined in this solution by the usual method (see Deter-
mination of Copper in Ordinary Brass).1

4.  Determination   of  the Iron, Nickel   and   Zinc.—5 grams   of
the sample are treated with nitric acid (D = 1-2), the solution being left
on the water-bath for a short time and then filtered ; the filtrate is treated
with excess of sulphuric acid and evaporated to complete elimination of
the nitric acid.   The residue is taken up in water, filtered, treated with
hydrogen sulphide and filtered again, the filtrate being u'sed for the deter-
mination of the iron, zinc and nickel as in argentan.

1 It should be borne in mind that cadmium may sometimes be present as well as
copper.d then withoncen- the elec-